September 29, 2004

Pumpe Duse
by Jim Kerr

When most people think of diesel engines, they think of clouds of black smoke, noisy operation and sluggish acceleration. That image no longer applies. Today's diesel engines are high tech, much cleaner, quieter and provide snappy performance. High injection pressures and computer controls have revamped the way diesel engines operate. Now Volkswagen is building a new type of diesel engine fuel system that improves vehicle performance even more. They call it "Pumpe Duse". Translated, it means "pump injectors".

Most current high tech passenger vehicle diesels use a common rail injection system. Similar to gasoline injection but operating at much higher pressures, the common rail system has one gear driven high pressure fuel pump that supplies fuel to fuel rails or pipes, which in turn provide fuel to all the injectors at the same time. Typical fuel rail pressures are in the 14,000 to 16,000 PSI at idle and go over 20,000 PSI under heavy load conditions.

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Just like the gasoline injectors, a computer controls the opening time and injection duration by operating an electric solenoid inside the injector. This solenoid then causes a metal valve to move that allows the fuel to spray out the tip of the injector. This is a simplified description. There are many parts inside these high pressure diesel injectors but it is easiest to think of them as being similar to gasoline injection.

Volkswagen's Pumpe Duse or pump injectors also use a computer controlled electric solenoid to control injector opening and duration but there the similarity stops. Instead of one high pressure pump for the fuel system, each Pumpe Duse injector is its own high pressure pump.

Fuel is supplied to each Pumpe Duse injector from a low pressure fuel pump and lines. A camshaft and rocker arms on the cylinder head operate a plunger with return spring on the top of the injector body that produce the high fuel pressure. This high pressure fuel is then injected, with injection controlled by the computer.

One of the advantages the Pumpe Duse injection system has the high pressure it operates at. With up to 30,000 PSI injection pressure, considerably higher than common rail systems, the Pumpe Duse injector provides finer atomisation of the fuel for high torque and power with low emissions and high fuel efficiency. The Pumpe Duse diesels are capable of converting up to 43 per cent of the thermal energy in the fuel into mechanical energy. This is better than for any other liquid-fuelled production car.

The economy and performance of the Pumpe Duse system can be found in many Volkswagen models but is perhaps best demonstrated by the Touareg SUV. The Touareg offers an aluminium alloy V10 diesel engine that produces 310 horsepower and 553 ft lbs of torque. This power propels this 2642 kilogram SUV from 0 to 100 kph in just 7.5 seconds yet still achieves a Transport Canada fuel economy rating of 10.8 litres per 100 km on the highway.

Another advantage of the Pumpe Duse system is the elimination of the common rail high pressure pump and lines. With a common rail system, if there is a leak in any fuel line or one injector develops a leak either internal or external, all the injectors are affected. It takes only the smallest leak to cause a "No Start" condition because no fuel pressure can be generated to allow the injectors to spray. With the Pumpe Duse system, a problem at one injector is isolated from the others.

One thing is common to all the current high pressure diesel injection systems: they require clean fuel. Even the smallest foreign particles in the fuel or any water will cause wear on the injectors. This wear can occur internally in the injector valves or at the spray nozzle tip. The high pressure of the fuel flowing through the injector combined with water or dirt acts like a cutting torch on the metal.

The fix for this problem is to replace the faulty injectors - a costly repair. Fortunately, prevention is the best solution. Use clean fuel from clean fuel tanks. Those tanks often seen in the backs of pickup trucks are often contaminated with both water and dirt so you are wiser to fill at a service station pump than store your own fuel. Another key preventative step is to change fuel filters often. If you wait until performance starts to degrade, the filters are already full and injector damage is likely. While today's diesel engines operate cleaner with better performance than ever before, the fuel system tolerances are much tighter. More frequent fuel filter changes are essential to injector life.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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